How Do Endosperm Proteins Affect the Pasting and Texture of Rice? – A Study of the Physiochemical Properties of Rice Using a Model System

Abstract

Protein is the second most abundant component of rice, but its influence on the physiochemical properties of rice is not clear. Albumin, globulin, prolamin and glutelin were added separately to rice starch at pre-determined concentrations, and the pasting and textural properties of the resultant mixtures were analysed by the Rapid ViscoAnalyser (RVA) and the TA XT2 Textual Analyser. Addition of albumin to rice starch caused significant (P < 0.01) increases in all the pasting parameters measured and the textural property of gel hardness, but significant decreases in gel adhesiveness. In contrast, addition of globulin caused significant (P < 0.01) decreases in all the pasting parameters and gel adhesiveness, but increases in hardness. For the two storage proteins, increasing the concentration of prolamin in starch resulted in decreases in pasting temperature, peak and final viscosities, gel hardness and adhesiveness, but increases in breakdown viscosity. In contrast, increasing the concentration of glutelin resulted in decreases in peak, breakdown and final viscosities, but increases in pasting temperature, gel hardness and adhesiveness. A model rice system was created by adding to rice starch albumin, globulin, prolamin and glutelin in different ratios and the pasting and textural properties of the resultant model rice flour were compared with those of rice starch control. The results show that the physiochemical properties of the model rice system are broadly comparable with native rice of similar composition. Our results indicate that such a model system can be a useful tool for studying the physiochemical properties of rice.